This invention relates to a process for expanding tobacco to increase its filling capacity, i.e., to reduce its bulk density. The process is particularly suitable for treating cigarette cut filler.
During curing, tobacco leaf loses moisture and shrinks. Subsequent storage and treatments such as cutting contribute to the shrunken or collapsed condition of the entire leaf, particularly the thin lamina portion which is used for cut filler.
Prior to about 1970, several processes were suggested or proposed for increasing filling capacity of tobacco. No commercial success was reported as to such pre-1970 process. In 1970, U.S. Pat. No. 3,524,451 to Fredrickson, and U.S. Pat. No. 3,524,452 to Moser et al. were granted. These patents describe commercially significant processes for expanding or puffing tobacco by contacting the tobacco with a volatile impregnant and then heating the tobacco by rapidly passing a stream of hot gas in contact therewith to volatilize the impregnant and expand the tobacco. These flash-expansion processes have now been widely accepted and put into extensive commercial use throughout the world.
A variation of these processes is described in subsequently issued U.S. Pat. No. 3,683,937 to Fredrickson et al. which discloses a process for puffing or expanding tobacco by contacting the tobacco with vapors of a volatile impregnant while maintaining the temperature above the boiling point of the impregnant at the prevailing pressure so that the tobacco remains free of any liquid or solid form of the impregnant and thereafter rapidly reducing the pressure or rapidly increasing the temperature to provide vapor releasing conditions and expansion of the tobacco. This patent reported tobacco expansion employing Freon-12 as an impregnant with heating of the impregnated tobacco at a temperature of 56.degree. C. in a closed apparatus at a pressure of 202 psig. The thus pressurized and impregnated tobacco was expanded by rapidly venting the closed apparatus to the atmosphere without a subsequent heating step. A filling capacity increase of 60 percent was reported.
U.S. Pat. No. 4,235,250 to Utsch, along with U.S. Pat. No. 4,258,729 to Burde et al. and U.S. Pat. No. 4,336,814 to Sykes et al. disclose the use of carbon dioxide as the expansion agent in a process wherein tobacco is treated with carbon dioxide gas or liquid to impregnate the tobacco, and thereafter the carbon dioxide-impregnated tobacco is subjected to rapid heating conditions to volatilize the carbon dioxide and thereby expand the tobacco.
U.S. Pat. No. 4,696,313 to Brown et al. discloses a process similar to the Fredrickson et al. '937 process wherein tobacco is impregnated with a liquid impregnant and heated in a closed vessel. The temperature and pressure conditions achieved in the vessel are such that the temperature is above the boiling point temperature of the impregnating agent at the pressure achieved in the closed vessel. Thereafter, the pressure is suddenly vented from the first vessel into a second vessel to expand the tobacco. This patent reports increases in filling volume of tobacco/tobacco stem mixtures ranging from 52 percent to 70 percent. A similar process which employs a mixture of volatile expansion agents, one of which is water soluble and the other of which is water insoluble, is disclosed in U.S. Pat. No. 4,641,655 to Hedge et al. while an apparatus for conducting such expansion processes is described in U.K. Patent Application 2,183,442A to Brown et al., published June 10, 1987.
U.S. Pat. No. 4,531,529 to White et al. discloses a process for increasing filling capacity of tobacco by contacting the tobacco with an expansion agent at or near supercritical conditions of pressure and temperature and thereafter rapidly reducing the pressure to provide tobacco expansion without subjecting the tobacco to additional heat.
The tobacco expansion processes which employ a postheating step are known to affect the taste of the tobacco. This is believed due to loss of some volatile components during the post-impregnation heating step. Similarly, with those processes which do not employ a post-heating step, if the temperature is relatively high during impregnation and subsequent pressure reduction of the treated tobacco, volatile components of the tobacco can be lost during the pressure reduction step.